1. Field of the Invention
The present invention relates generally to sound control systems and more particularly to the acoustical performance of faced ceiling systems.
2. Background Information
In modern structures, such as residential or commercial buildings, an important issue for a designer to consider is the adequacy of sound absorption in interior rooms. Sound absorption can be defined as the total energy of incident sound minus that of reflected sound, and the amount of sound absorption provided by elements in a room (such as carpeting, furniture, etc.) can greatly affect an occupant's acoustic comfort level. For example, in a room or space that allows excessive echo or reverberation (i.e., persistence of sound after the sound source has stopped producing sound), speech comprehension can be difficult if not impossible.
The ability of a material or system for absorbing sound can be expressed in units of Noise Reduction Coefficient or NRC, as described by the American Society of Testing and Materials (ASTM), where a system of 0.90 NRC has about 90% absorbing ability of an ideal absorber, for example. NRC ratings are calculated for a system by averaging determined sound absorption coefficients specified at ⅓ octave band center frequencies of 250, 500, 1000, and 2500 Hz.
Reverberation time is a unit for measuring echo in a space and indicates the period of time required for a sound level to decrease 60 decibels after the sound source has stopped. The amount of sound absorption necessary for a particular space depends, of course, on the primary uses of the space. For spaces where a reduction in reverberation time is critical (such as large meeting rooms, dining areas, auditoriums, or teleconferencing rooms), sound absorption areas and locations are adjusted to achieve the reverberation time that suits the room use by strategically distributing prescribed sound absorbing panels and tiles over the walls, ceiling, and possibly the floor. Such a treatment enhances intelligibility and sound diffusion in the room and, in many cases, the use of sound absorbing panels optimized for sound absorption in the speech frequencies (around 250 to 2,000 Hz), can provide a satisfactory reverberation time and preserve necessary signal-to-noise ratios without amplification.
For spaces where factors other than sound control dominate the design, such as rooms in an office building, ceiling tiles are typically utilized as the only major sound absorbing elements. While these conventional tiles possess some sound absorbing ability (e.g., an NRC rating of 0.55), designers are sometimes forced to use further acoustical insulation in the forms of batting installed above ceiling tiles or additional ceiling and/or wall sound panels to reduce distracting noises associated with human conversation and office equipment, and to increase employee privacy and productivity. Unfortunately, these methods are expensive, attach additional bulk to a structure's design, and require time-consuming and accurate installation.
Ceiling tiles are typically covered on their interior side (i.e., the side facing occupants of a room) with a facing material that has the sole purpose of making the tiles aesthetically pleasing or at least unobtrusive. To date, such facing material has not been addressed as an important element of an acoustical system.
A method of superimposing a facing sheet with a substrate to augment the acoustical properties of the substrate is disclosed in U.S. Pat. No. 5,824,973 (Haines et al.), hereby incorporated by reference in its entirety. The Haines patent, however, requires a complicated and particularized determination of each substrate's optimized value of acoustic resistance ratio, where a facing material of a calculated air flow resistance is only superimposed on a substrate if it is determined that the substrate has an insufficient air flow resistance to optimize the value of the acoustic resistance ratio.